Leetcode Algorithm

Single Number

Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.

Follow up: Could you implement a solution with a linear runtime complexity and without using extra memory?

Example 1:

Input: nums = [2,2,1]
Output: 1

Example 2:

Input: nums = [4,1,2,1,2]
Output: 4

Example 3:

Input: nums = [1]
Output: 1

Constraints:

• 1 <= nums.length <= 3 * 104
• -3 * 104 <= nums[i] <= 3 * 104
• Each element in the array appears twice except for one element which appears only once.

Solutions:

Python —

class Solution:
    def singleNumber(self, nums:List[int])-> int:
        # create a set
        hashset = set()
        for i in range(0, len(nums)):
            if nums[i] in hashset:
                hashset.remove(nums[i])
            else:
                hashset.add(nums[i])
        for j in hashset:
            return j;

JS —

var singleNumber= function(nums){
    const set1 = new Set();
    for (i = 0; i < nums.length; i ++){
        if (set1.has(nums[i]))
            set1.delete(nums[i]);
        else
            set1.add(nums[i]);
}
    for (let item of set1){
        return item;
}
};

Link

Reference for JS solution